linux+cycles+cuda: nvcc fatal: Value 'sm_52' is not defined for option 'gpu-architecture'
Two reasons:


The cuda-7.0 toolkit installer failed to properly set permissions, so blender can't see the nvcc from the proper location.
When blender can't read using the symlink cuda in /usr/local/cuda/bin/nvcc it seems to search for nvcc using cuda-&lt;version&gt;/ instead. But it does it in the wrong order, also without reporting the permission issue.


Without others-readable permissions on /usr/local/cuda-7.0/, the symlink /usr/local/cuda fails and blender tries /usr/local/cuda-6.0/bin/nvcc even though a newer /usr/local/cuda-6.5/bin/nvcc exists.

The solution:

sudo chmod -R o+rX /usr/local/cuda-7.0/


Had no other toolkits been installed the error would have been:

which: no nvcc in ($PATH)
CUDA nvcc compiler not found. Install CUDA toolkit in default location.